Adhesive compositions, adhesive articles and methods for making the same

ABSTRACT

Adhesive compositions comprising a high molecular weight acrylic copolymer and a low molecular weight copolymer are disclosed. Adhesive articles and methods of making adhesive compositions and articles are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Application Ser. No.12/304,186, filed Jun. 19, 2007, now pending, which is national stagefiling under 35 U.S.C. 371 of PCT/US2007/071551, filed Jun. 19, 2007,which claims priority to U.S. Provisional Patent Application No.60/815,078, filed Jun. 20, 2006, the disclosures of which areincorporated by reference in their entirety herein.

FIELD

The present disclosure relates to adhesive compositions comprising ahigh molecular weight acrylic copolymer and a low molecular weightacrylic copolymer.

SUMMARY

In one aspect, the present disclosure is directed to adhesivecompositions comprising a blend of a first acrylic copolymer and asecond acrylic copolymer. In one exemplary embodiment, the adhesivearticle comprises a blend of a first acrylic copolymer resulting frompolymerization of monomers A and B, wherein (i) the first acryliccopolymer has a number average molecular weight, M_(n), of at leastabout 150,000 (or a weight average molecular weight, M_(w), of at leastabout 450,000), and (ii) monomer B has at least one reactive group thatis capable of hydrogen bonding. The second acrylic copolymer resultsfrom polymerization of monomers C and D, wherein (i) the second acryliccopolymer has a number average molecular weight, M_(n), of less thanabout 70,000 (or a M_(w) less than about 100,000), (ii) monomer D has atleast one reactive group that is capable of hydrogen bonding, and (iii)the second acrylic copolymer comprises greater than about 10 parts byweight (pbw) of monomer D based on a total weight of the second acryliccopolymer. In some embodiments, the pbw of monomer D in the secondacrylic copolymer is greater than the pbw of monomer B in the firstacrylic copolymer. In some embodiments, the pbw of monomer D in thesecond acrylic copolymer is at least about 3 pbw greater than the pbw ofmonomer B in the first acrylic copolymer.

In a further exemplary embodiment of the present disclosure, theadhesive article comprises a blend of (1) a first acrylic copolymerformed from monomers A and B, wherein the first acrylic copolymer (i)has a number average molecular weight, M_(n), of at least about 150,000(or a M_(w) of at least about 450,000) and (ii) comprises less thanabout 10 percent by weight (pbw) of monomer B based on a total weight ofthe first acrylic copolymer, wherein monomer B has at least one reactivegroup that is capable of hydrogen bonding; and (2) a second acryliccopolymer formed from monomers C and D, wherein the second acryliccopolymer (i) has a number average molecular weight, M_(n), of less thanabout 70,000 (or a M_(w) less than about 100,000) and (ii) comprisesgreater than about 10 pbw of monomer D based on a total weight of thesecond acrylic copolymer.

In yet a further exemplary embodiment of the present disclosure, theadhesive article comprises an adhesive foam layer comprising a mixtureof a first acrylic copolymer and a second acrylic copolymer, wherein thefirst acrylic copolymer (i) is formed from monomers A and B, whereinmonomer B has at least one reactive group that is capable of hydrogenbonding, (ii) has a number average molecular weight, M_(n), of at leastabout 150,000 (or a M_(w) of at least about 450,000) and (iii) comprisesless than about 10.0 percent by weight (pbw) of monomer B based on atotal weight of the first acrylic copolymer; and the second acryliccopolymer (i) is formed from monomers B and C, (ii) has a number averagemolecular weight, M_(n), of less than about 70,000 (or a M_(w) of lessthan about 100,000) and (iii) comprises a percent by weight (pbw) ofmonomer B based on a total weight of the second acrylic copolymer,wherein the pbw of monomer B of the second acrylic copolymer is greaterthan the pbw of monomer B of the first acrylic copolymer.

In another aspect, the present disclosure provides adhesive articlescomprising one or more adhesive core layers and, optionally, one or moreadditional layers. In one exemplary embodiment of the presentdisclosure, the adhesive article comprises (a) an adhesive core layercomprising the above-described blend or mixture of a first acryliccopolymer having a relatively high molecular weight and a second acryliccopolymer having a relatively low molecular weight; and (b) at least oneadditional layer on a major surface of the adhesive core layer. Theadhesive article of the present disclosure may further comprise otherlayers including, but not limited to, a second adhesive layer, such as apressure-sensitive adhesive layer and/or a heat-activatable adhesivelayer, at least one release liner, at least one non-adhesive substratelayer, or any combination thereof.

In another aspect, the present disclosure is further directed to methodsof making adhesive articles. In one exemplary embodiment, the method ofmaking an adhesive article comprises the steps of extruding a blend of(1) a first acrylic copolymer formed from monomers A and B, wherein thefirst acrylic copolymer (i) has a number average molecular weight,M_(n), of at least about 150,000 (or a M_(w) of at least about 450,000)and (ii) comprises less than about 10 percent by weight (pbw) of monomerB based on a total weight of the first acrylic copolymer, whereinmonomer B has at least one reactive group that is capable of hydrogenbonding; and (2) a second acrylic copolymer formed from monomers C andD, wherein the second acrylic copolymer (i) has a number averagemolecular weight, M_(n), of less than about 70,000 (or a M_(w) of lessthan about 100,000) and (ii) comprises greater than about 10 pbw ofmonomer D based on a total weight of the second acrylic copolymer; andexposing the extrudate to an amount of irradiation so as to obtain acontrolled degree of crosslinking between the first acrylic copolymerand the second acrylic copolymer. Desirably, the controlled degree ofcrosslinking between the first acrylic copolymer and the second acryliccopolymer results in a crosslinked adhesive article having a stressrelaxation ratio G(300)/G(0.1) as measured by a Stress Relaxation Testat 70° C. of less than or equal to about 0.30, desirably, from about0.13 to about 0.30.

In another exemplary embodiment, the method of making an adhesivearticle comprises providing an electron beam generating apparatus havinga first control for an accelerating voltage and a second control for adose; providing a material to be cured having a composition, athickness, and a density; determining one or more desired propertiescapable of resulting from a controlled amount of crosslinking using theelectron beam generating apparatus; and using a Minimum Calculated CoreCure value of the material based on dose-depth profile calibrationcurves for the electron beam generating apparatus and for the materialto be cured, crosslinking the material at a voltage and dose thatresults in the one or more desired properties. The exemplary method mayfurther comprise preparing the dose-depth profile calibration curves forthe electron beam generating apparatus and for the material to be curedbased on the composition, thickness, and density of the material; anddetermining the Minimum Calculated Core Cure value based on thedose-depth profile calibration curves.

These and other features and advantages of the present disclosure willbecome apparent after a review of the following detailed description ofthe disclosed embodiments and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary adhesive articleaccording to some embodiments of the present disclosure;

FIG. 2 is a cross-sectional view of an exemplary tape according to someembodiments of the present disclosure in roll form comprising anexemplary adhesive article having a removable release liner on an outersurface thereon;

FIG. 3 is a schematic drawing of an exemplary extrusion process forpreparing adhesive articles according to some embodiments of the presentdisclosure;

FIG. 4 provides an exemplary graph showing electron beam radiation doseversus tape depth for the sample tape of Example 1 after electron beamradiation exposure to one outer surface;

FIG. 5 provides an exemplary graph showing electron beam radiation doseversus tape depth for the sample tape of Example 1 after electron beamradiation exposure to both outer surfaces;

FIG. 6 provides an exemplary graph showing electron beam radiation doseversus tape depth for the sample tape of Example 1 after electron beamradiation exposure to both outer surfaces at a lower acceleratingvoltage than used in the trial shown in FIG. 5;

FIG. 7 provides an exemplary graph showing Stress Relaxation at 70° C.versus Minimum Calculated Core Cure for sample tapes of Examples 1-8;and

FIG. 8 provides an exemplary graph showing Stress Relaxation at 70° C.versus the product of the Average Calculated Core Cure (ACCC) and theMinimum Calculated Core Cure (MCCC) for sample tapes of Examples 1-8.

DETAILED DESCRIPTION

Generally, the adhesive compositions of the present disclosure comprisea mixture of a high molecular weight acrylic copolymer and a lowmolecular weight acrylic copolymer. In some embodiments, the adhesivecompositions may optionally further comprise one or more additionalcomponents as described below.

The high molecular weight acrylic copolymer is also referred to hereinas the “first acrylic copolymer.” The first acrylic copolymer is formedfrom monomer(s) A and monomer(s) B. As used herein, the term“monomer(s)” indicates that one or more monomers may be selected. Forexample, “monomer(s) A” may include one or more monomers selected fromthose monomers suitable for use as a monomer A. Similarly, “monomer(s)B” refers to the one or more monomers selected from those monomerssuitable for use as a monomer B.

Suitable monomers for monomer A include, but are not limited to, acrylicor methacrylic esters of non-tertiary alkyl alcohols, with the alkylgroups having from 1 to 20 carbon atoms (for example, from 3 to 18carbon atoms). Such monomers A include, but are not limited to,methyl(meth)acrylate, ethyl(meth)acrylate, n-butyl(meth)acrylate,lauryl(meth)acrylate, 2-ethylhexyl(meth)acrylate,cyclohexyl(meth)acrylate, isooctyl(meth)acrylate,octadecyl(meth)acrylate, tridecyl(meth)acrylate, nonyl(meth)acrylate,decyl(meth)acrylate, dodecyl(meth)acrylate, isobornyl(meth)acrylate,2-phenoxyethyl(meth)acrylate, benzyl(meth)acrylate,n-hexyl(meth)acrylate, n-octyl(meth)acrylate, phenyl(meth)acrylate, orany combination thereof. As used herein, the term “(meth)acrylate” isused to refer to either one or both of the acrylate and methacrylatespecies. For example, methyl(meth)acrylate refers to methyl acrylate,methyl methacrylate, and combinations thereof.

Suitable monomers for monomer B include, but are not limited to,acrylic, methacrylic, or other unsaturated acids with the alkyl grouphaving from 1 to 20 carbon atoms (for example, from 3 to 18 carbonatoms). Such monomers B include, but are not limited to, acrylic acid,methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric,acid, and itaconic, citraconic, maleic and fumaric monoesters (these arediacid compounds and their monoester offer an acid group), or anycombination thereof. Other suitable monomers B include acrylonitrile,methacrylonitrile, vinyl acetate, N-vinyl pyrrolidone, isobornylacrylate, cyano ethyl acrylate, N-vinylcaprolactam, maleic anhydride,hydroxyalkylacrylates, N,N-dimethyl aminoethyl(meth)acrylate,N,N-diethylacrylamide, vinylidene chloride, styrene, vinyl toluene,hydroxyarylacryaltes, tetrahydrofurfuryl(meth)acrylate, and alkyl vinylethers.

In some embodiments, at least one monomer B comprises a monomer havingat least one reactive group thereon that is capable of hydrogen bonding(for example, —COOH).

In some embodiments, the first acrylic copolymer comprises less thanabout 10 percent by weight (pbw) of monomer(s) B based on a total weightof the first acrylic copolymer. In some embodiments, the first acryliccopolymer comprises from about 2 to about 7 pbw of monomer(s) B based ona total weight of the first acrylic copolymer.

The high molecular weight acrylic copolymer component (or first acryliccopolymer) may be formed using conventional polymerization techniques.These techniques are generally known in the industry and includeprocesses such as thermally initiated polymerization, photoinitiation,suspension polymerization, and the like. Typically, in addition tomonomer(s) A and monomer(s) B, an appropriate polymerization initiatorcan be used to initiate polymerization of monomers A and B. Suitableinitiators for photoinitiation include, but are not limited to,2,2-dimethoxy-2-phenylacetophenone (for example, IRGACURE™ 651commercially available from Ciba-Geigy (Hawthorne, N.Y.));2-hydroxy-1-(4-*2-hydroxyethoxy)phenyl)-2-methyl-1propanone (forexample, DAROCURE™ 2959 commercially available from Ciba-Geigy);2-hydroxy-2-methyl-1-phenyl-1-propanone (for example, DAROCURE™ 1173commercially available from Ciba-Geigy); diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (for example, LUCIRIN™ TPOcommercially available from BASF Corporation (Florham Park, N.J.));1-hydroxycyclohexyl phenyl ketone (for example, IRGACURE™ 184commercially available from Ciba-Geigy); 2-methyl-1-(4-(methythio)phenyl)-2-(4-morpholinyl)-1-propanone (for example, IRGACURE™ 907commercially available from Ciba-Geigy);2-benzyl-2-(dimethylamino)-1-(4-(4-morpholinyl)phenyl)-1-butanone (forexample, IRGACURE™ 369 commercially available from Ciba-Geigy);phenylbis (2,4,6-trimethyl benzoyl)- phosphine oxide (for example,IRGACURE™ 819 commercially available from Ciba-Geigy), or ethyl2,4,6-trimethylbenzoylphenylphosphinate (for example, LUCIRIN™ TPO-Lcommercially available from BASF Corporation).

Further, a chain transfer agent may be present during the polymerizationreaction. Chain transfer agents may be used to control the molecularweight of the resulting polymer and reduce the amount of residualmonomer remaining after the polymerization reaction. Suitable chaintransfer agents include, but are not limited to, isooctyl thioglycolate(IOTG) (for example, IOTG commercially available from Daicel ChemicalIndustries, LTD (Tokyo, JAPAN) or from Dow Chemical Company (Midland,Mich.)); n-octyl mercaptan (for example, commercially available fromArkema (Philadelphia, Pa.); n-decyl mercaptan (for example, commerciallyavailable from Philips Petroleum (Houston, Tex.)); n-hexyl mercaptan(for example, commercially available from Arkema); n-octadecyl mercaptan(for example, commercially available from ACIMA Chemical Industries(Philadelphia, Pa.)); n-dodecyl mercaptan (for example, commerciallyavailable from Arkema); tert-dodecyl mercaptan (for example,commercially available from Arkema); and 2-ethylhexyl thioglycolate (forexample, commercially available from Arkema).

In some embodiments, the first acrylic copolymer has a number averagemolecular weight, M_(n), of at least about 150,000. In some embodiments,the first acrylic copolymer has a weight average molecular weight, M_(w)of at least about 450,000. As used herein, number average molecularweight, M_(n), and weight average molecular weight, M_(w), are measuredusing the Gel Permation Chromatography (GPC) test method described inthe “Test Methods” section below.

In some embodiments, the first acrylic copolymer has a M_(n) rangingfrom about 150,000 to about 600,000 (and/or a M_(w) of at least about450,000 to about 2,000,000). In some embodiments, the first acryliccopolymer has a M_(n) ranging from about 160,000 to about 350,000(and/or a M_(w) of at least about 480,000 to about 1,000,000) and insome embodiments, a M_(n) from about 170,000 to about 300,000 (and/or aM_(w) of at least about 500,000 to about 900,000).

Generally, the first acrylic copolymer may be present in an amount thatvaries depending on the desired properties of the resulting adhesivecomposition. Typically, the first acrylic copolymer is present in anamount greater than about 50 percent by weight (pbw) based on a totalweight of the adhesive composition. In some embodiments, the firstacrylic copolymer is present in an amount greater than about 60, greaterthan about 65, or even greater than about 70 pbw. In some embodiments,the first acrylic copolymer is present in an amount ranging from about75 to about 98 pbw, based on a total weight of the adhesive composition.

Adhesive compositions according to the present disclosure furthercomprise a low molecular weight acrylic copolymer, also referred toherein the “second acrylic copolymer.” The second acrylic copolymer isformed from monomer(s) C and monomer(s) D. Suitable monomers for monomerC are the same as those suitable for monomer A, and are described abovewith respect to the first acrylic copolymer. Similarly, suitablemonomers for monomer D are the same as those suitable for monomer B, asdescribed above with respect to the first acrylic copolymer.

Generally, each of the monomer(s) A, B, C, and D are independentlyselected. In some embodiments, one or more of the monomers selected foruse as monomer(s) A may also be selected for use as monomer(s) C.Similarly, in some embodiments, one or more monomers selected for use asmonomer(s) B may also be selected for use as monomer(s) D.

In some embodiments, the second acrylic copolymer comprises greater thanabout 10 pbw of monomer(s) D based on a total weight of the secondacrylic copolymer. In some embodiments, the second acrylic copolymercomprises from about 12 to about 30 pbw of monomer(s) D, and, in someembodiments, from about 15 to about 20 pbw of monomer(s) D, based on atotal weight of the second acrylic copolymer.

Typically, the pbw of monomer(s) D of the second acrylic copolymer isgreater than the pbw of monomer(s) B of the first acrylic copolymer. Insome embodiments, the pbw of monomer(s) D of the second acryliccopolymer is at least 3 pbw greater than the pbw of monomer(s) B of thefirst acrylic copolymer. In other embodiments, the pbw of monomer(s) Dof the second acrylic copolymer is at least 5 pbw (or at least 8 pbw, orat least 10 pbw, or at least 12 pbw, or at least 15 pbw) greater thanthe pbw of monomer(s) B of the first acrylic copolymer.

In some embodiments, at least one monomer C of the second acryliccopolymer is identical to at least one monomer A of the first acryliccopolymer. In some embodiments, all of the monomer(s) C of the secondacrylic copolymer are the same as the monomer(s) A of the first acryliccopolymer. In other embodiments, each monomer C of the second acryliccopolymer differs from all of the monomer(s) A of the first acryliccopolymer.

In some embodiments, the second acrylic copolymer is substantially freeof “photoinitiator monomers,” that is, (i) monomers containing reactivegroups that are susceptible to forming radicals in the presence of aphotoinitiator and (ii) monomers, which are themselves photoactiveradical formers. In such an exemplary embodiment, the second acryliccopolymer is formed from monomers C and D, and possibly additionalmonomers, as long as the additional monomers are not photoinitiatormonomers. In some embodiments, the first acrylic copolymer is alsosubstantially free of photoinitiator monomers.

The low molecular weight acrylic copolymer component (that is, thesecond acrylic copolymer) may be formed using conventionalpolymerization techniques as discussed above with regard to the highmolecular weight acrylic copolymer component (or first acryliccopolymer). In addition to monomer(s) C and monomer(s) D, apolymerization initiator and/or chain transfer agent may be presentduring the polymerization reaction.

In some embodiments, the second acrylic copolymer has a number averagemolecular weight, M_(n), of less than about 70,000. In some embodiments,the second acrylic copolymer has weight average molecular weight, M_(w),of less than about 100,000. In some embodiments, the second acryliccopolymer has a number average molecular weight, M_(n), ranging fromabout 10,000 to about 70,000 (and/or a M_(w) of from about 14,000 toabout 100,000). In some embodiments, the second acrylic copolymer has anumber average molecular weight, M_(n), ranging from about 15,000 toabout 60,000 and/(or a M_(w) of from about 20,000 to about 84,000), and,in some embodiments, a M_(n) of from about 20,000 to about 55,000(and/or a M_(w) of from about 28,000 to about 77,000).

The second acrylic copolymer may be present in an amount that variesdepending on the desired properties of the resulting adhesivecomposition. Typically, the second acrylic copolymer is present in anamount less than about 50 pbw based on a total weight of the adhesivecomposition. In some embodiments, the second acrylic copolymer ispresent in an about less than about 40 pbw, or less than about 35 pbw,or even less than about 30 pbw. In some embodiments, the second acryliccopolymer is present in an amount ranging from about 25 to about 2 pbw,based on a total weight of the adhesive composition.

In some embodiments, various additives or other ingredients may be addedto the adhesive composition to impart or modify particularcharacteristics of the ultimate adhesive composition. The additives maybe present in any amount as long as the amount does not adverselyinterfere with the desired properties of the adhesive composition. Insome embodiments, the adhesive composition comprises one or moreadditives in an amount of up to about 50 weight percent, based on thetotal weight of the adhesive composition. Exemplary additives include,but are not limited to, tackifiers, plasticizers, fillers, antioxidants,pigments, diffusing materials, fibers, filaments, silicas, treatedsilicas, carbon black, dyes, expandable polymeric microspheres,non-expandable polymeric or glass microspheres, chain transfer agents,chemical blowing agents, reinforcing agents, calcium carbonate,toughening agents, fire retardants, acrylate-insoluble polymers, finelyground polymeric particles such as polyester, nylon, or polypropylene,stabilizers, and combinations thereof.

In one exemplary embodiment, the adhesive composition comprises a foamhaving voids throughout at least a portion of the adhesive composition.Voids may be formed by incorporating a variety of additives into theadhesive core layer prior to or during formation of the adhesive corelayer. For example, expandable polymeric microspheres, hollow polymericor glass microspheres, foaming agents, or any combination thereof may beincorporated into the adhesive core layer in order to form voidsthroughout at least a portion of the adhesive core layer. Suitablevoid-forming materials include, but are not limited to, void-formingmaterials disclosed in U.S. Pat. No. 6,103,152. In some embodiments,expandable polymeric microspheres, such as those disclosed in U.S. Pat.No. 6,103,152, are incorporated into the adhesive composition in anamount ranging from about 1 pbw to about 15 pbw, and, in someembodiments, from about 2 pbw to about 6 pbw, based on a total weight ofthe adhesive composition.

In some embodiments, the adhesive composition may be an outermost layerof the adhesive article. In some embodiments, the adhesive compositionmay be sandwiched between two or more similar or dissimilar substrates.

In some embodiments, the adhesive articles of the present disclosurecomprise one or more layers with at least one layer, for example, a corelayer, being formed from an adhesive composition comprising acrosslinkable or crosslinked mixture of high and low molecular weightacrylic copolymers. As shown in FIG. 1, exemplary adhesive article 40comprises adhesive core layer 41 having first major surface 42 andsecond major surface 44. In some embodiments, adhesive article 40includes at least one of first additional layer 43 on first majorsurface 42, and second additional layer 45 on second major surface 44.Exemplary adhesive article 40 further comprises first outer majorsurface 46 on first additional layer 43 and second outer major surface48 on second additional layer 45.

Generally, the adhesive core layer comprises an intimate mixture (orblend) of the above-described first and second acrylic copolymers. Insome embodiments, the first and second acrylic copolymers are mixed withone another so as to result in a desired degree of hydrogen bondingbetween the first and second acrylic copolymers. In some embodiments,the first and second acrylic copolymers are mixed so as to result in adegree of hydrogen bonding that provides an adhesive core having adesired amount of stress relaxation, while maintaining desiredperformance during high temperature shear.

In some embodiments, the first and second acrylic copolymers aresubstantially miscible with one another so that the resulting mixturecomprises a single phase or domain. In other embodiments, the first andsecond acrylic copolymers, when mixed, form two separate phases ordomains intimately blended with one another. In either case, theresulting mixture provides a degree of hydrogen bonding between thefirst and second acrylic copolymers.

In one exemplary embodiment in which the first and second acryliccopolymers are extruded with one another, the polymers may be immisciblewith one another so that small domains of each polymer are present inthe extrudable mixture. By minimizing the time between mixing andextruding or by using in-line static mixing, extrusion of the adhesivemixture can occur before any substantial amount of phase separationtakes place. By cooling the extrudate in a relatively rapid manner, thefirst and second acrylic copolymers remain in an intimate mixture, whichcan then be subsequently crosslinked as described below.

In some embodiments, the adhesive composition possesses a stressrelaxation ratio (G(300)/G(0.1)) value (that is, “SRR value”) of lessthan about 0.3, and in some embodiments, from about 0.1 to about 0.3, asmeasured by the “Stress Relaxation Test” conducted at 70° C. (asdescribed below in the “Test Methods” section). The SSR value of a givenadhesive composition provides an indication of the ability of theadhesive to (i) deform under continuous load and (ii) resist deformationas the adhesive extends under the continuous load. FIG. 7 provides anexemplary graph showing the change in SRR values of various polymercompositions as the amount of exposure to electron beam radiationincreases. The controlled amount of exposure to electron beam radiationis measured as a minimum calculated core cure (“MCCC”) amount asdescribed in the “Test Methods” section below.

The calculated cure is dependent on the specific equipment used todeliver the electron beam, and those skilled in the art can define adose calibration model for the equipment used. For example, in thepresent disclosure, the radiation processing is performed on an EnergySciences, Inc. (Wilmington, Mass.), Model CB-300 electron beamgenerating apparatus equipped with a 76.2 micrometer (μ) (0.003 inch)thick, 30.48 millimeter (mm) (12 inch) wide polyester terephthalatesupport film running through an inert chamber as described below.

In one exemplary embodiment, adhesive compositions may have a SSR valueof less than about 0.35, and in some embodiments, from about 0.1 toabout 0.3, after exposure to electron beam radiation. In a furtherexemplary embodiment, the adhesive composition has a SSR value of lessthan about 0.28, for example, from about 0.12 to about 0.25, or evenfrom about 0.15 to about 0.23, after exposure to electron beamradiation.

As discussed above, in some embodiments, the adhesive compositioncomprises a foam core layer. Solid adhesive core layers (that is,non-foam layers) typically have a layer density ranging from about 0.92g/cc to about 1.2 g/cc, while adhesive foam core layers, themselves,typically have a layer density ranging from about 0.3 g/cc to about 0.7g/cc. Typically, articles resulting from the combination of one or moreskin layers with the adhesive core layers have an overall densityranging from about 0.4 grams per cubic centimeter (g/cc) to about 0.8g/cc.

In some embodiments, the adhesive composition exhibits resistance to astatic shear load, which is measured by a hanging shear test (describedin the “Test Methods” section below). Hanging shear measures the abilityof a defined area of a pressure sensitive adhesive (PSA) adhesive bondedbetween two rigid surfaces to hold a fixed weight hanging from one edgeof one of the surfaces without substantially sliding apart (fallingoff). It is usually measured in minutes of hang time with a given area,(typically about either 323 sq mm or 635 sq mm) and a given load(typically 500g/323 sq mm or 1000g/625 sq mm at 70° C. or 2 kg/625 sqmm. at room temperature).

In some embodiments, the adhesive composition of the present disclosureremain intact after 5,000 minutes, and, in some embodiments, after10,000 minutes with a 500 gram weight hanging from one panel both at 70°C. and at room temperature. The 70° C. temperature objective istypically more difficult to meet.

In addition to the adhesive core layer described above, in someembodiments, the present disclosure provides adhesive articles that mayinclude one or more additional layers on either side of the adhesivecore layer. The one or more additional layers may each independently betemporarily or permanently attached to an outer surface of the adhesivecore layer. Suitable additional layers are described below.

Referring to exemplary adhesive article 40 shown in FIG. 1, firstadditional layer 43 and/or second additional layer 45 could be adhesivelayers. The one or more additional adhesive layers may be any suitableadhesive known in the art, including, for example, an adhesive that isactivatable by pressure, heat or a combination thereof. Suitableadhesives include, but are not limited to, adhesive compositionscomprising (meth)acrylate copolymers, rubber/resins, epoxies, urethanesor combinations thereof. Each additional adhesive layer may be appliedto an outer surface of the adhesive core layer by any known methodincluding, for example, by solution, water-based or hot-melt coatingmethods, including hot melt co-extrusion methods where one or morelayers are formed simultaneously with the above-described adhesive corelayer. Each additional adhesive layer may include hot melt coatedformulations, transfer-coated formulations, solvent-coated formulations,and latex-coated formulations, as well as, laminating,thermally-activated, and water-activated adhesives and bonding agents.In some embodiments, at least one of the additional adhesive layers,when present, comprises a pressure sensitive adhesive (PSA), aheat-activatable adhesive layer (for example, a hot melt adhesivelayer), or a combination thereof.

Examples of suitable pressure sensitive adhesives include, but are notlimited to, PSAs based on general compositions of poly(meth)acrylate;polyvinyl ether; diene rubber such as natural rubber, polyisoprene, andpolybutadiene; polyisobutylene; polychloroprene; butyl rubber;butadiene-acrylonitrile polymer; thermoplastic elastomer;

block copolymers such as styrene-isoprene and styrene-isoprene-styrene(SIS) block copolymers, ethylene-propylene-diene polymers, andstyrene-butadiene polymers; poly-alpha-olefin; amorphous polyolefin;silicone; ethylene-containing copolymer such as ethylene vinyl acetate,ethylacrylate, and ethyl methacrylate; polyurethane; polyamide; epoxy;polyvinylpyrrolidone and vinylpyrrolidone copolymers; polyesters; andmixtures or blends (continuous or discontinuous phases) of the above.

Examples of suitable heat-activatable adhesives include, but are notlimited to, heat-activatable adhesives based on general compositions ofpolyolefins, copolymers containing olefin monomers, etc.

As discussed with regard to the adhesive core layer above, eachadditional adhesive layer adhesive composition may contain additives.

In some embodiments, the adhesive article comprises an adhesive corelayer in combination with at least one additional adhesive layer,wherein the at least one additional adhesive layer is present on a majorsurface of the adhesive core layer in the form of a PSA layer. In afurther exemplary embodiment, the adhesive article comprises an adhesivecore layer in combination with PSA layers on both major surfaces of theadhesive core layer. In either of these embodiments, the PSA maycomprise a PSA containing a styrene-isoprene asymmetric star blockcopolymer such as disclosed in U.S. Pat. No. 5,393,787 issued toNestegard et al., U.S. Pat. No. 6,503,621 issued to Ma et al., or U.S.Pat. No. 6630,531, issued to Khandpur et al., all of which are assignedto 3M Innovative Properties Company (St. Paul, Minn.), the subjectmatter of which is hereby incorporated herein in its entirety.

In addition to the adhesive core layer and any optional additionaladhesive layers described above, the adhesive articles may include oneor more release liners to protect an outer surface of an adhesive corelayer or any additional adhesive layer of the adhesive article.

As shown in FIG. 2, exemplary adhesive article 50 comprises adhesivecore layer 51 having first major surface 52 and second major surface 54,release liner 53 on first major surface 52, and an additional layer 55on second major surface 54. Exemplary adhesive article 50 furthercomprises first outer major surface 56 on additional layer 55, andrelease liner inner surface 58 and release liner outer surface 60 onrelease liner 53.

Release liners are well-known in the art, and any known release linermay be used. Typically, the release liner comprises a film or papersubstrate coated with a release material. Commercially available releaseliners include, but are not limited to, silicone coated papers, andsilicone coated films, such as polyester films. Examples of suitablerelease liners include, but are not limited to, release liners soldunder the trade designation AKROSIL™ available from Akrosil Europe(Huerlen, Netherlands) and International Paper (Menasha, Wis.); andrelease liners available from Daubert Coated Products, Inc. (Dixon,Ill.). In some embodiments, the release liner comprises AKROSIL™ PaperLiner ZG-3223 (Akrosil Europe, Huerlen, Netherlands) or AKROSIL™ PaperLiner SBL 60 SC SILOX FlU/F4B (International Paper, Menasha, Wis.).

In one exemplary embodiment, the above-described adhesive articlecomprises a release liner as disclosed in U.S. Pat. Nos. 6,835,422;6,805,933; 6,780,484; or 6,204,350 assigned to 3M Innovative PropertiesCompany.

Referring again to FIG. 2, it should be noted that release liner 53 mayprovide release properties along release liner inner surface 58, releaseliner outer surface 60, or both. For example, if additional layer 55 isan additional adhesive layer, such as a PSA, release liner outer surface60 of release liner 53 will desirably have release properties. If firstouter major surface 56 on additional layer 55 does not have any degreeof adhesive tackiness, release liner outer surface 60 of release liner53 does not need release properties.

In a further embodiment, additional layer 55 on second major surface 54of adhesive core layer 51 also comprises a release liner such thatrelease liner 53 and additional layer 55 protect protection to firstmajor surface 52 and second major surface 54 of adhesive core layer 51.

In some embodiments, adhesive articles of the present disclosure mayalso include one or more additional layers that may provide additionaltemporary or permanent properties to the adhesive articles. Suitableadditional layers may be positioned on one or both sides of the adhesivecore layer. In some embodiments, the one or more additional layers areflexible such that the resulting adhesive article may be rolled into aroll. The one or more additional layers may function as, for example,tie layers, primer layers, or barrier layers. Suitable additional layersinclude, but are not limited to, polymer films, metal foils, papers,foam sheets, and fabrics. The one or more additional layers may beattached to the adhesive core layer by a pressure-sensitive adhesive asdescribed above or by the adhesive core layer composition itself.

Examples of suitable substrates include, but are not limited to, glass,metal, plastic, wood, and ceramic substrates, painted surfaces of thesesubstrates, and the like. Representative plastic substrates includepolyester, polyvinyl chloride, ethylene-propylene-diene monomer rubber,polyurethanes, polymethyl methacrylate, engineering thermoplastics (forexample, polyphenylene oxide, polyetheretherketone, polycarbonate), andthermoplastic elastomers. The substrate may also be a woven or knittedfabric formed from threads of synthetic or natural materials such as,for example, cotton, nylon, polyamide, rayon, glass, carbon or ceramicmaterial. The substrate may also be made of a nonwoven fabric such asair-laid webs of natural or synthetic fibers or blends thereof

The present disclosure also provides methods of making adhesivecompositions and articles. In one exemplary embodiment, the method ofmaking an adhesive composition comprises mixing the above-describedadhesive composition components. Desirably, the components are mixed toform a substantially homogeneous adhesive composition mixture. Themethod may further comprise a number of optional steps depending on theultimate use of the adhesive composition. For example, the method maycomprise a method of forming an adhesive article, wherein the methodcomprises shaping the adhesive composition into an adhesive article (forexample, a coating step or an extrusion step). In addition, post-shapingsteps may be used to impart desired physical properties to the shapedadhesive article. For example, the method of forming an adhesive articlemay further comprise exposing a portion of the shaped adhesive articleto radiation in order to crosslink one or more components within theshaped adhesive article.

Exemplary methods of making adhesive compositions and adhesive articlesare described below.

Adhesive core layers may be prepared using conventional method stepssuch as those disclosed in U.S. Pat. No. 6,103,152 issued to Gehlsen.Typically, the method of making an adhesive article comprising at leastone adhesive core layer comprises melt-mixing the above-describedadhesive components to form a substantially homogeneous mixture, shapingthe substantially homogeneous mixture to form a shaped adhesive article,and allowing the shaped adhesive article to cool. In some embodiments,the shaping step may comprise providing the adhesive composition mixtureonto a temporary substrate (for example, a release liner) or permanentsubstrate (for example, a backing layer or other adhesive layer), forexample, by a coating step. In other embodiments, the shaping step maycomprise providing the adhesive composition mixture onto a temporarysubstrate (for example, a release liner) or permanent substrate (forexample, a backing layer or other adhesive layer) via an extrusion step.

In one embodiment, the method of forming an adhesive article comprisesan extrusion step. FIG. 3 depicts an extrusion apparatus suitable foruse in some methods of the present disclosure. In this exemplaryembodiment, each of the above-described copolymers (for example, firstand second acrylic copolymers) may be initially fed into a first heatingand conveying device 10 such as a roll feeder, single screw extruder (asshown), grid melter, or bonnot, where input materials, such as each ofthe copolymers are melted. The copolymers may be added to heating andconveying device 10 in any convenient form, including pellets, billets,packages, strands, and ropes. At the end the heating and conveyingdevice, is typically, a metering device (not shown), such as a gear meltpump, where the output rate of the melted polymer can be controlled. Atthe end of the metering pump, a heated hose (not shown) may be used toconvey the metered output to, for example, a twin screw extruder 12.Twin screw extruder 12 is typically fitted with ports (not shown) alongits length, for inputting metered liquids, such as melted copolymers,tackifiers, stabilizers, and the like, usually under pressure. Twinscrew extruder 12 also has open ports 13 that are not under pressure,where dry solids, such as stabilizers, pigments, rubbers and/or plasticpellets, expandable microspheres, and the like can be supplied. The drysolid materials are typically conveyed to open port 13 via a weight lossfeeder (not shown) to control the feed rate. Along the length of thetwin screw extruder 12 are mixing kneaders and/or conveying sections,which allow control of the degree of mixing of the separately fedmaterials. Various sections of the twin screw extruder 12 can be heatedor cooled to control the temperature of the mixing and conveyingprocess, as well as the twin screw turning rate.

Desirably, mixing is carried out at a temperature insufficient to causesubstantial microsphere expansion within the twin screw extruder 12 forembodiments in which expandable microspheres are present during mixing.For example, mixing temperatures may be from about 100° C. to about 125°C. In other embodiments, it is also possible to use temperatures inexcess of a microsphere expansion temperature (for example, mixingtemperatures may be from about 125° C. to about 160° C.) either becausethe pressures of the extruder/mixing/conveying process preventsubstantial expansion until the mixture reaches the coating head orbecause the temperature can be reduced prior to adding the microspheres.In actual practice, some of the expandable microspheres can be brokenduring mixing, and such conditions may be optimized to minimizebreakage. Specific temperatures, pressures, shear rates, and mixingtimes are selected based upon the particular composition beingprocessed.

At the end of the extruder is, typically, a gear melt pump 16, whichprovides an output stream free of pressure surges. The metered output istypically fed via a heated pipe or hose 18 to a coating head, such as adie 14 (for example, a contact or drop die). Optionally, an in-linemixing device (not shown), such as a static mixer, may be used tooptimize the mixture and temperature homogeneity, especially if theheated pipe or hose 18 is long. The temperature and pressure within die14 is desirably controlled to cause expansion of expandable microspheres(when present) within the die lips, as the composition exits the coatinghead 14 and experiences the pressure drop to normal atmosphericconditions.

The shape of the adhesive core layer is dictated by the shape of die 14.Although a variety of shapes may be produced, the adhesive core layer istypically produced in the form of a continuous or discontinuous sheethaving outer major surfaces separated from one another by a peripheraledge.

As shown in FIG. 3, the adhesive core layer 23 may optionally becombined with a temporary or permanent layer 20 (for example, a releaseliner) dispensed from a feed roll 22. Suitable temporary layers forlayer 20 include, but are not limited to, silicone release liners,polyester films (for example, polyethylene terephthalate films), andpolyolefin films (for example, polyethylene films), as well as otherrelease layers described above. Layer 20 and the adhesive core layer arethen laminated together between a pair of nip rollers 24. Followinglamination, the adhesive core layer is optionally exposed to radiationfrom an electron beam source 26 to crosslink the adhesive core layer.The electron beam can be provided from one or both sides of the corelayer either through a temporary or permanent layer, or directly onto anexposed surface of the core layer. Other sources of radiation (forexample, ion beam, gamma radiation, and ultraviolet radiation) may beused as well. Crosslinking improves the cohesive strength of theadhesive core layer. Following exposure, the laminate is rolled up toform a take-up roll 28.

In some embodiments, the method of forming an adhesive article comprisesexposing the adhesive core layer to electron beam radiation so as toprovide a controlled amount of crosslinking between the first and secondacrylic copolymers of the adhesive core layer. Depending on thethickness and density of the adhesive composition, a particularaccelerating voltage and dose of the electron beam is directed at theadhesive mass from one or both sides of the sheet so that the resultingadhesive core layer has a desired balance of properties, for example,shear strength, stress relaxation, and the like.

In some embodiments, the method of forming an adhesive article comprisesextruding a blend of the first acrylic copolymer and the second acryliccopolymer; and exposing the extrudate to an amount of irradiation so asto obtain a controlled degree of crosslinking between the first acryliccopolymer and the second acrylic copolymer. In some embodiments, theresulting adhesive article has a stress ratio G(300)/G(0.1) as measuredby a Stress Relaxation Test at 70° C. of less than about 0.30, and , insome embodiments, from about 0.10 to about 0.30 as discussed above.

Further, as discussed above, the relative amounts (that is, pbw) ofmonomer(s) B and D in the first and second acrylic copolymers,respectively, may be varied so as to provide a desired degree ofhydrogen bonding between the first and second acrylic copolymers. Asdiscussed above, in some embodiments, the pbw of monomer(s) D in thesecond acrylic copolymer is greater than the pbw of monomer(s) B in thefirst acrylic copolymer, and, in some embodiments, at least about 3 pbwgreater than the pbw of monomer B in the first acrylic copolymer.

In some embodiments, the method of making an adhesive article comprisesproviding an electron beam generating apparatus having a first controlfor an accelerating voltage and a second control for a dose; providing amaterial to be cured having a composition, a thickness, and a density;determining one or more desired properties capable of resulting from acontrolled amount of crosslinking using the electron beam generatingapparatus; and using a Minimum Calculated Core Cure value of thematerial based on dose-depth profile calibration curves for the electronbeam generating apparatus and for the material to be cured, crosslinkingthe material at a voltage and dose that results in the one or moredesired properties. For example, the one or more desired properties maycomprise stress relaxation, shear strength, or a combination thereof.This exemplary method may further comprise preparing the dose-depthprofile calibration curves for the electron beam generating apparatusand for the material to be cured based on the composition, thickness,and density of the material; and determining the Minimum Calculated CoreCure value based on the dose-depth profile calibration curves. Asdescribed in the Examples below, a Monte Carlo code can be used toassist in the determination of the Minimum Calculate Core Cure value.

The exemplary method of making an adhesive article using a MinimumCalculated Core Cure value of the material based on dose-depth profilecalibration curves for the electron beam generating apparatus and forthe material to be cured desirably utilizes a cure procedure thatresults in a cure gradient through a cross section of the thickness ofthe material being cured. Typically, the material to be cured is in theform of a sheet having a given sheet thickness. Desirably, at least oneof the dose-depth profile calibration curves for the cured materialexhibits a minimum within a middle 80% of the thickness of the material,more desirably, within a middle 50% of the thickness of the material.Further, at least one of the dose-depth profile calibration curves forthe cured material exhibits a concave downward profile.

The exemplary method of making an adhesive article using a MinimumCalculated Core Cure value of the material based on dose-depth profilecalibration curves for the electron beam generating apparatus and forthe material to be cured can be used to make an adhesive article, suchas the above-described adhesive article comprising a blend of high andlow molecular weight acrylic copolymers. In one exemplary method, thematerial to be cured comprises a blend of (1) the first acryliccopolymer and (2) the second acrylic copolymer; wherein the pbw ofmonomer(s) D in the second acrylic copolymer is greater than the pbw ofmonomer(s) B in the first acrylic copolymer.

The present disclosure is also directed to methods of makingmulti-layered articles comprising at least one adhesive core layer. Theadhesive core layer may be combined with one or more additional layersusing conventional techniques including, but not limited to, lamination,coating, coextrusion, etc. Suitable additional layers include layersdescribed above.

In some embodiments, multi-layered adhesive articles are desirablyformed by co-extruding the above-described extrudable adhesivecomposition containing first and second acrylic copolymers with one ormore extrudable polymer compositions. The number and type of polymercompositions are selected based upon the desired properties of the finaladhesive article. For example, in the case of adhesive core layershaving relatively low tack at room temperature (for example, theadhesive core layer is not a PSA), it may be desirable to combine theadhesive core layer with one or more PSA compositions to form anadhesive article having outer surface tack at room temperature. Otherexamples of polymer compositions that may be prepared by co-extrusioninclude, but are not limited to, relatively high modulus polymercompositions for stiffening the article (semi-crystalline polymers suchas polyamides and polyesters), relatively low modulus polymercompositions for increasing the flexibility of the article (for example,plasticized polyvinyl chloride), and additional foam compositions.

In one embodiment, the method of making multi-layered articles comprisesa coextrusion step wherein additional extrudable polymer compositionsare coextruded with the above-described extrudable adhesivecompositions. FIG. 3 illustrates one coextrusion process for producing amulti-layered article comprising an adhesive core layer sandwichedbetween a pair of additional layers. As shown in FIG. 3, polymer resinis optionally added to a first extruder 30 (for example, a single screwextruder) where it is softened and ground into particles. The resinparticles are then fed to a second extruder 32 (for example, a single ortwin screw extruder) where they are mixed with any desired additives.The resulting extrudable composition is then metered to the appropriatechambers of die 14 through transfer tubing 34 using a gear pump 36. Theresulting article is a three-layer article featuring an adhesive corelayer having a polymer layer on each of its major surfaces (see, forexample, such a three-layer article in FIG. 1, namely exemplary adhesivearticle 40).

It is also possible to conduct the co-extrusion process such that atwo-layer adhesive article is produced, or such that adhesive articleshaving more than three layers (for example, 10-100 layers or more) areproduced by equipping die 14 with an appropriate feed block, or by usinga multi-vaned or multi-manifold die. Multilayer adhesive articles canalso be prepared by laminating additional layers to the adhesive corelayer, or to any of the co-extruded polymer layers after the adhesivearticle exits die 14. Other techniques which can be used include stripecoating.

Various adhesive articles of the present disclosure may be used in anumber of applications. As described above, the adhesive articles maycomprise a single adhesive core layer or may comprise one or more layersin addition to an adhesive core layer. The adhesive articles may bepresent in the form of a strip, tape, roll of tape, or any otherconstruction known in the art. The adhesive articles may be bonded toone or more substrates to provide a multi-layered article having adesired degree of contact between the adhesive article and one or moresubstrates bonded thereto.

In some embodiments, the adhesive articles may be particularly useful ina variety of applications, including aerospace, automotive, and medicalapplications. The properties of the adhesive articles may be tailored tomeet the demands of the desired applications. Specific examples ofapplications include, but are not limited to, vibration dampingarticles, medical dressings, tape backings, retroreflective sheetbackings, anti-fatigue mats, abrasive article backings, gaskets, andsealants.

Various exemplary embodiments of the present disclosure are describedabove and further illustrated below by way of examples, which are not tobe construed in any way as imposing limitations upon the scope of theinvention. On the contrary, it is to be clearly understood that resortmay be had to various other embodiments, modifications, and equivalentsthereof which, after reading the description herein, may suggestthemselves to those skilled in the art without departing from the spiritof the present invention and/or the scope of the appended claims.

EXAMPLES

These examples are merely for illustrative purposes only and are notmeant to be limiting on the scope of the appended claims. All parts,percentages, ratios, etc. in the examples and the rest of thespecification are by weight unless indicated otherwise.

As used herein, a sheet generally refers to a sheet of material(s), suchas a foam sheet, that typically has a thickness of at least about 5mils. A film generally refers to a thinner sheet typically having athickness of about 5 mils or less. A tape generally refers to a sheetthat has been cut into a narrower width. In the examples, the termssheet, film and tape may be used interchangeably.

Test Methods: Gel Permation Chromatography (GPC)

Gel Permation Chromatography was used to determine the molecular weightsof the polymers. A sample of the resulting polymer was removed from thepackage and Gel Permeation Chromotography was performed on the sampleaccording to the manufacturer's general instructions and the followingprocedure to determine the molecular weight. Three samples weighingapproximately 25 milligrams (mg) were tested for each of the polymers.Each sample was dissolved in 10.00 ml of tetrahydrofuran over a threeday period, and then filtered using a 0.25 micron Gelman PTFE syringefilter. A WATERS Alliance 2695 Separations Module (available fromWaters, Inc. (Milford, Mass.)) was used to inject 100 microliters ofeach sample solution into a two column set (available from JordiAssociates Inc. (Bellingham, Mass.)). One column was equipped with amixed bed and the other with a 500A column, both 25 cm). The WATERS 2695chromatograph was operated at room temperature, using tetrahydrofuran asthe eluent, flowing at a rate of 1.0 ml/min. A Shimadzu Scientific Inc.(Columbia, Md.) RID-10A refractive index detector was used to detectchanges in the concentration. The molecular weight calculations werebased on calibrations made of narrow polystyrenes ranging in molecularweight from 7.50×10⁶ to 580.

Minimum Calculated Core Cure (MCCC)

The Minimum Calculated Core Cure (MCCC) was used as a measure of thecontrolled amount of electron beam radiation delivered at various depthsthrough a thickness cross section of a specific material, for example, asheet or tape, having a specific composition, thickness, and density.The electron beam dose at a given accelerating voltage was plottedagainst thickness to obtain a dose-depth profile having a minimum inapproximately the center portion of the cross section of the tape.Separate samples of each tape construction were treated to a differentdose and accelerating voltage. The minimum cure in approximately thecenter of the core, that is, the dose delivered to that part of thecore, was calculated for each tape and process conditions. The averagecure throughout the thickness of the tape was also calculated for anAverage Calculated Core Cure (ACCC). The samples were tested for one ormore desired end properties, for example, stress relaxation and hangingshear strength in this case. Stress relaxation expressed as the StressRelaxation Ratio (SRR) was then plotted as a function of the MinimumCalculated Core Cure. The SRR was also plotted as a function of theproduct (Prod) of the ACCC and the MCCC. The product provides somewhatmore delineation of the values in the plots and is consistent with theplot of just MCCC. Monte Carlo code was used to help predict the depthand dose values based on the apparatus and the tape construction, thatis, the composition, thickness, and density, to facilitate adjustment ofthe electron beam dose at various depths to allow delivery of theoptimal dose to obtain the desired end product. This methodology isdescribed in U.S. Pat. No. 6,749,903, the subject matter of which ishereby incorporated herein in its entirety.

The calculated cure depends on the specific equipment used to deliverthe electron beam, and those skilled in the art can define a dosecalibration model for the equipment used. For the examples describedherein, the radiation processing was performed on a Model CB-300electron beam generating apparatus (available from Energy Sciences, Inc.(Wilmington, Mass.) equipped with a 0.076 mm (0.003 inch) thick, 30.48cm (12 inch) wide polyester terephthalate support film running throughan inert chamber. A sample of a tape with a liner on both sides wastaped onto the support film and conveyed at a speed of about 6.1meters/min (20 feet/min) such that the tape was treated from one sidethrough the polyethylene release liner. A thicker sample, such as a foamtape, may exhibit a cure gradient through the cross section of the tapeso that it is desirable to expose the tape to electron beam radiationfrom both sides. For the examples, the tape was treated from both sidesby turning the sample over after one pass through the machine andconveying it through the machine again. This provided a controlled doseto the central portion of the adhesive tape to effect crosslinking andhence, temperature resistance. The oxygen level within the chamber ofthe CB-300 was restricted to a range of 50 to 100 ppm. The standardnitrogen gap between the window and the web path was 47 mm and the samemachine settings were used on each pass through the machine.

Prior to treating samples, the electron beam apparatus was calibratedaccording to ASTM E 1818 with dosimetry using 10 micron and 45 microndosimeters, which are polymeric films containing radiochromic dye,commercially available from Far West Technologies, Inc. (Goleta,Calif.). The calibration provided a measure of surface dose and adose/depth profile as a function of accelerating voltage and beamcurrent. The actual sample dose is the energy deposited into a squarecentimeter of substrate divided by the density of the sample, so thedose-depth profile for substrates having different densities than thedosimeters were normalized. A dose-depth profile was calculated for eachtape construction (which typically has a liner, a foam core of aspecific composition, and optional skin layers of specific compositionson the foam core) to account for the differences in densities of thedifferent layers that the electron beam must penetrate to reach thecenter of the tape. Samples tested for Stress Relaxation Ratio (SRR)were representative of the thickness and density of the samples thatreceived a specified dose at a specified accelerating voltage. Thethickness and density measurements were typically made immediatelyadjacent to the area from which the SRR measurements were made.

Stress Relaxation Ratio-G(300)/G(0.1)—(SRR)

The Stress Relaxation Ratio (G(300)/G(0.1) test was used to characterizethe time dependent behavior of an adhesive article, for example, a tapesample, when a constant level of shear strain is applied to a sample.The shear modulus of a sample was measured at specific time intervalsduring the test. When the test was completed, a ratio was calculatedusing the modulus at 300 seconds divided by the modulus at 0.1 seconds(G(300)/G(0.1)). This “stress ratio” provides an indication of amaterial's “firmness” (for example, the material's response under load).

The Stress Relaxation Ratio (G(300)/G(0.1) test was performed using anAdvanced Rheometric Expansion System (ARES) (available from TAInstruments (New Castle, Del.)) with a 25 mm Parallel Plate TestFixture. The rheometer was equipped with RSA Orchestrator software. Thetape sample was a circular disc having a diameter of 24.5 mm (1 inch)and a thickness of approximately 0.51 mm (20 mil). For samples thinnerthan 0.51 mm, several layers may be laminated together to provide therequisite thickness. The test was run at 70° C. (+/−1° C.) with a 1 mmgap and 25% strain. The data was recorded on a chart of the modulus (G)over time (seconds). The Stress Relaxation Ratio was calculated bydividing the modulus (G) at 300 seconds by the modulus at 0.1 second.

Hanging Shear

The Hanging Shear test was used as an indication of a tape's internalcohesive strength at elevated temperature. A sample of tape measuring2.54 cm by 1.27 cm was laminated to an etched aluminum panel measuring2.54 cm by 5.08 cm such that the tape edges were coextensive with edgesof the panels. The panel overlapped 1.27 cm to cover the tape and thefree ends of the panels extended in opposite directions. One end of apanel was hung on a rack in an oven set at 70° C. with a 500 gram weighthanging from the bottom of the end of the other panel so that the tapesample was under shear stress. The time for the bottom panel to releasefrom the hanging panel was measured up to 10,000 minutes. Test resultsare reported as Pass, that is, the panels were still adhered togetherafter 10,000 minutes in the oven, or Fail, that is, the bottom panel hadpulled away from the top panel in less than 10,000 minutes.

Pressure-Sensitive Adhesive Compositions

Packaged pressure-sensitive adhesive compositions were preparedaccording to the method described in U.S. Pat. No. 5,804,610, thesubject matter of which is hereby incorporated herein in its entirety,using the compositions and materials as listed below.

PSA-1—A pressure-sensitive adhesive (PSA) composition was prepared bymixing 45 parts of IOA (isooctyl acrylate), 45 parts of BA (butylacrylate), 10 parts of AA (acrylic acid), 0.15 part 2,2dimethoxy-2-phenylacetophenone (IRGACURE™ 651 available from CibaSpecialty Chemicals Corp. (Tarrytown, N.Y.)), and 0.06 part of IOTG(isooctyl thioglycolate). The composition was placed into packagesmeasuring approximately 10 cm by 5 cm by 0.5 cm thick as described in U.S. Pat. No. 5,804,610, the subject matter of which is herebyincorporated herein in its entirety. The packaging film was a 0.0635 mmthick ethylene vinyl acetate copolymer film (VA-24 Film available fromCT film (Dallas, Tex.)). The packages were immersed in a water bath andsimultaneously exposed to ultraviolet radiation at an intensity of about3.5 milliWatts per square centimeter, and a total energy of about 1680milliJoules per square centimeter as measured in NIST units. The PSAincluded both the polymer and the packaging film. The resulting polymer,that is, without the packaging film, had a M_(w) of about 5.75×10⁵ and aM_(n) of about 1.98×10⁵ as measured by the Gel Permeation Chromotographyprocedure described above.

PSA-2—A PSA composition was prepared according to the procedure abovefor PSA-1 except that the composition was 95 parts of 2-EHA(2-ethylhexyl acrylate), 5 parts of AA, 0.15 part IRGACURE™ 651photoinitiator, and 0.02 part of IOTG. The resulting polymer had in aM_(w) of about 5.54×10 ⁵ and a M_(n) of about 1.48×10 ⁵ when measuredaccording to the previously described GPC procedure.

PSA-3—A PSA composition was prepared according to the procedure forPSA-2 except for the following changes in the composition: 0.2 parts ofIRGACURE™ 651 photoinitiator, 0.8 parts of IOTG, and 0.4 part ofoctadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate (IRGANOX™1076 available from Ciba Specialty Chemicals Corp.) was added. A totalenergy of about 4107 mJ per sq cm was used. The resulting polymer had aM_(w) of about 5.54×10⁴ and a M_(n) of about 2.84×10⁴.

PSA-4—A PSA composition was prepared according to the procedure forPSA-3 except 0.3 parts of IOTG was used. A total energy of about 4107 mJper sq cm was used. The resulting polymer had a M_(w) of about 1.28×10⁵and a M_(n) of about 5.15×10⁴.

PSA-5—A PSA was prepared according to the procedure for PSA-3 exceptthat 85 parts of 2-EHA and 15 parts of AA were used and the total energyused was 1785 mJ per sq cm. The resulting polymer had a M_(w) of about4.72×10⁴ and a M_(n) of about 2.84×10⁴.

PSA-6—A PSA was prepared according to the procedure for PSA-5 exceptthat 0.3 part of IOTG was used, and the total energy was about 1778 mJper sq cm. The resulting polymer had a M_(w) of about 8.86×10⁴ and aM_(n) of about 5.72×10⁴.

PSA-7—A PSA was prepared according to the procedure for PSA-3 exceptthat 80 parts of 2-EHA and 20 parts of AA were used and the total energyused was 1778 mJ per sq cm. The resulting polymer had a M_(w) of about3.94×10⁴ and a M_(n) of about 2.54×10⁴.

PSA-8—A PSA was prepared according to the procedure for PSA 5 exceptthat 90 parts of 2-EHA, 10 parts of AA, and 0.03 part of IOTG were used.The total energy used was about 1530 mJ per square cm. The resultingpolymer had a M_(w) of about 5.75×10⁵ and a M_(n) of about 1.98×10⁵.

Skin Adhesive-1 (SA-1)

Skin Adhesive-1 was prepared by feeding about 12.7 parts of athermoplastic rubber (KRATON D-1340K, a multi-arm block copolymer withabout 9% styrene, obtained from Kraton Polymers, Inc. (Houston Tex), andmade according to U.S. Pat. No. 5,393,373, the subject matter of whichis hereby incorporated herein in its entirety) from a K-tron™ weightloss feeder into Zone 1 of a 40 mm Berstorff twin screw extruder having10 heated zones set at 120° C. The screw had conveying sections in zones1, 4, 8, 9, and 10, and mixing sections in the later portions of Zones2, 3, 5, 6, and 7. Other components were fed into different zones of theextruder using the feed equipment and temperatures as follows (allamounts are approximate as there are variations in the feeding devices,speed, etc.):

Zone 2: 6.2 parts of 2-ethylhexyl diphenyl phosphate plasticizer(SANTICIZER 141 available from Ferro Co. (Bridgeport, N.J.))—Zenithpump/hose with temperatures set at room temperature.

Zone 3: 23.2 parts of an aliphatic C-5 tackifying resin (EXCOREZ 1310LCavailable from ExxonMobil Chemical LTD. (Southampton, Hampshire,GB))—grid melter/melt pump/hose with temperatures set at 160° C.

Zone 4: 0.38 parts of black pigment having a 50/50 blend of carbon blackin ethylene vinyl acetate copolymer resin having a melt index of about150 (4900 CMB available from MA Hanna Color (Suwanee, Ga.)) fed from adisc doser.

Zone 5: 53.1 parts of PSA-1-51 mm Bonnot single screw extruder/meltpump/hose with temperatures set at 150° C.

Zone 6: 3.8 parts of a stabilized rosin acid ester tackifying resin(Superester W-115 available from Arakawa Chemical USA (Chicago, Ill.))mixed with 0.26 parts ofpentaerythritoltetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate(IRGANOX 1010 antioxidant available from Ciba Specialty Chemical Co.),and 0.26 parts of 2-(2-hydroxy-3,5-di-(tert)-amylphenyl)benzotriazole(TINUVIN 328 ultraviolet light absorber available from Ciba SpecialChemicals Co.)—grid melter/melt pump/hose with temperatures set at 160°C. The compounded adhesive was collected in a box lined with siliconerelease agent.

Skin Adhesive-2 (SA-2)

SA-2 was prepared according to the procedure for SA-1 except that 11.5parts of thermoplastic rubber (KRATON D-1340K), 20 parts of ESCOREZ1310LC tackifier, 55.6 parts of PSA-1, 6 parts of Superester W-115tackifier, and 3 parts of SANTICIZER 141 plasticizer were used.

Example 1

A foam core composition was prepared by feeding 97.7 parts of PSA-3 intozone 1 of a 40 mm Berstorff twin screw extruder having conveyingsections in zones 1, 4, 8, and 9, and mixing sections in the laterportions of zones 2, 3, 5, and 6. The extruder had 10 heated zones, eachset at 120° C. PSA-2 was fed from a 51 mm single screw extruder (Bonnot)apparatus having a melt pump and hose with temperatures set at 121°C./150° C./150° C. respectively. A K-tron™ T20 feeder was used to add2.3 parts of expandable microspheres having a shell compositioncontaining acrylonitrile and methacrylonitrile and a core of isopentane(DUALITE™ U010-185D expandable microspheres, available from SovereignSpecialty Chemicals Inc. (Avon, Ohio)). The microsphere-containingcompounded core was fed through a melt pump and hose, each set at about150° C., to the center port of a 25.4 cm (10 inch) wide Cloerenthree-layer adjustable vane type die with a keyhole shaped manifold setat a temperature of 192° C. The feed rate of the microspheres wasadjusted to achieve a particular target density.

A foam tape was prepared by feeding SA-1 (Skin Adhesive-1) at a rate ofabout 2.63 kg/hour to the outer layer port of the 3-layer Cloeren diefrom a 51 mm single screw extruder (Bonnot) with a melt pump and hoseset at temperatures of 150° C. The die vanes were adjusted to distributethe skin approximately equally to both sides of the die lips. The foamcore composition was fed to the center layer at about 11.35 kg/hour.Upon exiting the die, the co-extruded layers were cast onto a siliconerelease coated casting roll having a diameter of 18 inches and operatedat a surface speed of about 1.37 meters/minute. The roll was cooled withwater having a temperature of about 12° C. The cooled extrudate wastransferred from the casting roll to a 0.117 mm thick silicone coatedpolyethylene release liner that was transported at the same speed as thecasting roll to the end of the web transport line where it was cut intoapproximately 1.25 meter lengths. Another sheet of the same releaseliner was hand laminated to each sheet using a hand-held rubber rollerto exclude trapped air, and the sheets were stacked. The resulting foamtape had a total thickness of about 1.14 mm as measured with a digitalcaliper and a density of about 0.61 grams per cubic centimeter (g/cc).The skin adhesive layers on either side of the core had a thickness of0.076 mm (0.003 inch) and a density of about 0.98 g/cc, and the core hada thickness of about 0.99 mm (0.039 inch) and a density of about 0.98g/cc. The liners each had a thickness of 0.117 mm (0.0046 inch) and adensity of 0.99 g/cc.

The tape was irradiated with electron beam radiation at an acceleratingvoltage of 300 KeV and a dose of 10 megarads from one side of the tape.A plot of dose against tape thickness is shown in FIG. 4. The radiationwas not sufficient to crosslink the tape on the side of the tapeopposite the E-beam.

The sample was turned over and a second pass was made through the E-beamapparatus at the same accelerating voltage and dose. The resulting plotis shown in FIG. 5. The additive effect of the radiation in the middleof the tape was greater than at either surface so the resulting plot wasa convex curve.

The accelerating voltage was lowered to 230 KeV and a second sample ofthe tape was run through the apparatus twice. The additive effect of theradiation in the middle of the tape was less than at either surface sothe resulting plot had a concave downward profile with the minimumwithin about the central third of the cross section of the tape as shownin FIG. 6. The minimum, that is, the MCCC (Minimum Calculated CoreCure), was correlated to the shear strength and stress relaxation of thesample.

Five more samples of the same tape construction were treated withdifferent accelerating voltages and doses as shown in Table 1. Thestress relaxation and static shear strength were measured for eachprocess condition and the minimum e-beam cure in the cross section wascalculated according to the procedure for determining MCCC. The averagecure throughout the thickness of the tape was also calculated. Theproduct of the minimum core cure and the average core cure (Product) wascalculated. This product appears to provide a better resolution of thedata than just the minimum cure value alone. The stress relaxationvalues were plotted against the MCCC values for each dose as shown inFIG. 7. The stress relaxation was also plotted against the product ofthe Average Calculated Core Cure (ACCC) and the Minimum Calculated CoreCure (MCCC) as shown in FIG. 8.

Monte Carlo code was used to help select the accelerating voltage anddose for each sample. This example illustrates an exemplary method ofthe present disclosure wherein the Minimum Calculated Core Cure is usedto adjust the treatment level to meet the performance requirements of aparticular tape composition (liner, core, skin adhesives) and density.

Examples 2-8

Foam tapes were prepared according to the procedures described below.Two to five samples of each tape construction were exposed to differentelectron beam accelerating voltage in KeV and dose in MRads as indicatedby the letter after the Example number shown in Table 1. Each sample wasexposed to two passes through the apparatus so that both sides of thetape were irradiated. An e-beam dose/depth profile was calibrated foreach cured sample according to the procedure described above. TheMinimum Calculated Core Cure (MCCC) in megarads was determined as wellas the Average Calculated Core Cure (ACCC) in megarads and the Productof the MCCC and the ACCC. Representative samples of the cured tapecorresponding to each accelerating voltage and dose were measured forthickness and density, and tested for Shear Strength (SS) and StressRelaxation Ratio (SRR). Results are shown in Table 1. The StressRelaxation was plotted as a function of the Minimum Calculated Core Cureas shown in FIG. 7. The Stress Relaxation Ratio (SRR) was also plottedas a function of the Product of the Average Cure (Product) and theMinimum Cure as shown in FIG. 8.

The data shows how the stress relaxation characteristics of tapes havingvarying compositions can be controlled by the selection of theappropriate dose and accelerating voltage on an electron beam apparatusto provide the desired properties of the adhesive tape. The e-beamconditions were selected to provide a desired shear strength and stressrelaxation characteristic so that a process window can be established tomake tapes of a given composition, thickness, and density.

Example 2

A foam tape was prepared according to the procedure of Example 1 exceptas follows. The foam composition was prepared by feeding 84 parts ofPSA-2 from the single screw extruder to the twin screw extruder. Asimilar single screw extruder with temperatures set at 100° C./100°C./120° C. was used to feed 13.7 parts of PSA-3 into zone 2 of the twinscrew extruder. The casting roll speed was about 1.25 m/min. Theresulting foam tape had a total thickness of about 1.1 mm, and a densityof about 0.606 g/cc.

Example 3

A foam tape was prepared according to the procedure of Example 2 exceptthat the single screw extruder was used to feed 13.7 parts of PSA-4 intozone 2 of the twin screw extruder. The casting roll speed was about 1.22m/min. The resulting foam tape had a total thickness of about 1.16 mm,and a density of about 0.623 g/cc.

Example 4

A foam tape was prepared according to the procedure of Example 2 exceptthat the single screw extruder apparatus temperatures were set at 93°C./107° C./120° C., and about 13.7 parts of PSA-5 were fed into zone 2of the twin screw extruder. The casting roll speed was about 1.4 m/min.The resulting foam tape had a total thickness of about 1.09 mm, and adensity of about 0.623 g/cc.

Example 5

A foam tape was prepared according to the procedure of Example 4 exceptthat about 13.7 parts of PSA-6 were fed into zone 2 of the twin screwextruder. The casting roll speed was about 1.5 m/min. The resulting foamtape had a total thickness of about 1.13 mm, and a density of about0.637 g/cc.

Example 6

A foam tape was prepared according to the procedure of Example 4 exceptthat about 13.7 parts of PSA-7 were fed into zone 2 of the twin screwextruder. The casting roll speed was about 1.58 m/min. The resultingfoam tape had a total thickness of about 1.19 mm, and a density of about0.635 g/cc.

Example 7

A foam tape was prepared according to the procedure of Example 2 exceptthat about 83.2 parts of PSA-2 were fed into zone 1 of the twin screwextruder, about 13.5 parts of PSA-5 were fed into zone 2, and about 3.3parts of expandable microspheres were added to zone 8. The casting rollspeed was about 1.6 m/min. The resulting foam tape had a total thicknessof about 1.10 mm, and a density of about 0.55 g/cc.

Example 8

A foam tape was prepared according to the procedure of Example 4 exceptthat about 83.1 parts of PSA-8 were fed into zone 1 of the twin screwextruder, 15 parts of PSA-5 were fed into zone 2, and 1.9 parts ofexpandable microspheres were added to zone 8. The casting roll speed wasabout 1.3 m/min. The resulting foam tape had a total thickness of about1.14 mm, and a density of about 0.65 g/cc.

TABLE 1 Test Results Voltage- Dose Static Thickness Density MCCC ACCCProduct Ex KevD-Mrad Shear SRR mm g/cc Mrad Mrad Mrad 1A 238-9 Fail0.0906 44.8 0.6165 1.5 7.3 10.95 1B 240-10 Pass 0.1375 44.58 0.6065 2.58.3 20.75 1C 245-11 Pass 0.2073 44.77 0.6105 3.7 9.47 35.039 1D 250-11Pass 0.265 44.8 0.61 5.3 9.86 52.258 1E 277-11 Pass 0.4046 45.7 0.615211 11.705 128.755 2A 238-9 Fail 0.0364 45.75 0.6052 1.7 7.336 12.4712 2B240-10 Fail 0.0752 44.75 0.6046 2.5 8.3 20.75 2C 245-11 Fail 0.0961 46.50.604 3.6 9.443 33.9948 2D 260-11 Pass 0.2509 47.9 0.6089 6.5 10.3867.47 2E 277-11 Pass 0.3444 47.75 0.6033 10.5 11.58 121.59 3A 238-9 Fail0.0335 45.08 0.6213 1.6 7.309 11.6944 3B 240-10 Fail 0.0541 45.25 0.62132.1 8.242 17.3082 3C 245-11 Fail 0.119 45.48 0.6189 3.5 9.436 33.026 3D260-11 Pass 0.2454 46.52 0.625 6.5 10.392 67.548 3E 277-11 Pass 0.332946.5 0.6264 10.3 11.524 118.6972 4A 238-9 Fail 0.0500 41.52 0.62 2.57.42 18.55 4B 240-10 Fail 0.0530 44.08 0.626 2.1 8.19 17.199 4C 250-11Pass 0.1300 44.1 0.626 4.9 9.84 48.216 4D 264-11 Pass 0.18434 42.5 0.6239 11 99 4E 277-11 Pass 0.23313 42.72 0.62 11.8 11.93 140.774 5A 238-9Fail 0.0293 44.55 0.6384 1.1 7.18 7.898 5B 240-10 Fail 0.0468 44.650.6372 1.7 8.11 13.787 5C 258-10 Pass 0.15143 44.5 0.633 5.8 9.33 54.1145D 273-10 Pass 0.20871 44.1 0.6385 8.69 10.31 89.5939 5E 277-11 Pass0.2599 44.45 0.6317 10.7 11.6 124.12 6A 240-10 Fail 0.0322 47.27 0.64110.8 7.95 6.36 6B 258-10 Fail 0.08763 46.8 0.635 4.5 9.16 41.22 6C 273-10Pass 0.17505 44.05 0.6385 8.9 10.31 91.759 6D 277-11 Pass 0.1767 47.070.6355 9.3 11.26 104.718 7A 228-9 Fail 0.11017 37 0.5408 4.1 7.6 31.167B 236-10 Pass 0.16567 35.9 0.5297 7.4 9.3 68.82 8A 250-9 Pass 0.1015645.05 0.6615 2.7 7.77 20.979 8B 260-9 Pass 0.11692 44.55 0.6625 4.8 8.3640.128 8C 278-8.5 Pass 0.13335 45.5 0.6320 8 8.9 71.2

While the specification has been described in detail with respect tospecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

1. An adhesive article comprising a layer of an adhesive compositioncomprising a blend of: (i) a first acrylic copolymer resulting frompolymerization of one or more monomers A and one or more monomers B,wherein the first acrylic copolymer has a number average molecularweight, M_(n), ranging from about 150,000 to about 600,000; and (ii) asecond acrylic copolymer resulting from polymerization of one or moremonomers C and one or more monomers D, wherein the second acryliccopolymer has a number average molecular weight, M_(n), ranging fromabout 10,000 to about 70,000; wherein monomers B and monomers D have atleast one reactive group that is capable of hydrogen bonding; the secondacrylic copolymer comprises greater than about 10 total parts by weightof the monomers D based a total weight of the second acrylic copolymer;and the total parts by weight of the monomers D in the second acryliccopolymer is greater than the total parts by weight of the monomers B inthe first acrylic copolymer, and further wherein the adhesivecomposition is a cured, foam layer, and wherein the foam layer comprisesmicrospheres.
 2. The adhesive article of claim 1, wherein the adhesivecomposition has a stress relaxation ratio G(300)/G(0.1) as measured by aStress Relaxation Test at 70° C. of from about 0.10 to about 0.30 afterexposure to electron beam radiation.
 3. The adhesive article of claim 1,wherein the adhesive article passes a static shear test by maintaining ahanging load of 500 g for at least 10,000 minutes at 70° C.
 4. Theadhesive article of claim 1, wherein the adhesive article has a densityof from about 0.30 g/cc to about 0.80 g/cc.
 5. The adhesive article ofclaim 1, further comprising a first adhesive layer on a first outersurface of the layer of the adhesive composition and a second adhesivelayer on a second outer surface of the layer of the adhesive compositionopposite the first adhesive layer.
 6. The adhesive article of claim 1,further comprising a controlled degree of crosslinking between the firstacrylic copolymer and the second acrylic copolymer.
 7. A method ofmaking an adhesive article, said method comprising: providing anelectron beam generating apparatus having a first control for anaccelerating voltage and a second control for a dose; providing amaterial to be cured having a composition, a thickness, and a density;determining one or more desired properties capable of resulting from acontrolled amount of crosslinking using the electron beam generatingapparatus; and using a Minimum Calculated Core Cure value of thematerial based on dose-depth profile calibration curves for the electronbeam generating apparatus and for the material to be cured, crosslinkingthe material at a voltage and dose that results in the one or moredesired properties.
 8. The method of claim 7, further comprising:preparing the dose-depth profile calibration curves for the electronbeam generating apparatus and for the material to be cured based on thecomposition, thickness, and density of the material; and determining theMinimum Calculated Core Cure value based on the dose-depth profilecalibration curves.
 9. The method of claim 7, wherein the one or moredesired properties comprise stress relaxation, shear strength, or acombination thereof
 10. The method of claim 7, wherein the materialafter curing exhibits a cure gradient through a cross section of thethickness of the material.
 11. The method of claim 7, wherein thematerial comprises a blend of: (i) a first acrylic copolymer resultingfrom polymerization of one or more monomers A and one or more monomersB, wherein the first acrylic copolymer has a number average molecularweight, M_(n), ranging from about 150,000 to about 600,000; and (ii) asecond acrylic copolymer resulting from polymerization of one or moremonomers C and one or more monomers D, wherein the second acryliccopolymer has a number average molecular weight, M_(n), ranging fromabout 10,000 to about 70,000; wherein monomers B and monomers D have atleast one reactive group that is capable of hydrogen bonding; the secondacrylic copolymer comprises greater than about 10 total parts by weightof the monomers D based a total weight of the second acrylic copolymer;and the total parts by weight of the monomers D in the second acryliccopolymer is greater than the total parts by weight of the monomers B inthe first acrylic copolymer.